Nitrogen dioxide

Last updated
Nitrogen dioxide
Skeletal formula of nitrogen dioxide with some measurementsEP Nitrogen-dioxide-2D-dimensions-vector.svg
Skeletal formula of nitrogen dioxide with some measurementsEP
Spacefill model of nitrogen dioxide Nitrogen-dioxide-3D-vdW.png
Spacefill model of nitrogen dioxide
Nitrogen dioxide at different temperatures.jpg
NO
2 converts to the colorless dinitrogen tetroxide (N
2O
4) at low temperatures and reverts to NO
2 at higher temperatures.
Names
IUPAC name
Nitrogen dioxide
Other names
Nitrogen(IV) oxide, [1] deutoxide of nitrogen
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.030.234 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-272-6
976
PubChem CID
RTECS number
  • QW9800000
UNII
UN number 1067
  • InChI=1S/NO2/c2-1-3 Yes check.svgY
    Key: JCXJVPUVTGWSNB-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/NO2/c2-1-3
    Key: JCXJVPUVTGWSNB-UHFFFAOYAA
  • N(=O)[O]
  • [N+](=O)[O-]
Properties
NO•
2
Molar mass 46.005 g·mol−1
AppearanceBrown gas [2]
Odor Chlorine-like
Density 1.880 g/L [2]
Melting point −9.3 °C (15.3 °F; 263.8 K) [2]
Boiling point 21.15 °C (70.07 °F; 294.30 K) [2]
Hydrolyses
Solubility Soluble in CCl
4, nitric acid, [3] chloroform
Vapor pressure 98.80 kPa (at 20 °C)
+150.0·10−6 cm3/mol [4]
1.449 (at 20 °C)
Structure
C2v
Bent
Thermochemistry [5]
37.2 J/(mol·K)
Std molar
entropy (S⦵298)
240.1 J/(mol·K)
+33.2 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Poison, oxidizer
GHS labelling:
GHS-pictogram-rondflam.svg GHS-pictogram-acid.svg GHS-pictogram-skull.svg
Danger
H270, H314, H330
P220, P260, P280, P284, P305+P351+P338, P310
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
4
0
0
OX
Lethal dose or concentration (LD, LC):
30 ppm (guinea pig, 1  h)
315 ppm (rabbit, 15 min)
68 ppm (rat, 4 h)
138 ppm (rat, 30 min)
1000 ppm (mouse, 10 min) [6]
64 ppm (dog, 8 h)
64 ppm (monkey, 8 h) [6]
NIOSH (US health exposure limits):
PEL (Permissible)
C 5 ppm (9 mg/m3) [7]
REL (Recommended)
ST 1 ppm (1.8 mg/m3) [7]
IDLH (Immediate danger)
13 ppm [7]
Safety data sheet (SDS) ICSC 0930
Related compounds
Dinitrogen pentoxide

Dinitrogen tetroxide
Dinitrogen trioxide
Nitric oxide
Nitrous oxide

Contents

Related compounds
 Chlorine dioxide
Carbon dioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Nitrogen dioxide is a chemical compound with the formula NO2. One of several nitrogen oxides, nitrogen dioxide is a reddish-brown gas. It is a paramagnetic, bent molecule with C2v point group symmetry. Industrially, NO2 is an intermediate in the synthesis of nitric acid, millions of tons of which are produced each year, primarily for the production of fertilizers.

Nitrogen dioxide is poisonous and can be fatal if inhaled in large quantities. [8] Cooking with a gas stove produces nitrogen dioxide which causes poorer indoor air quality. Combustion of gas can lead to increased concentrations of nitrogen dioxide throughout the home environment which is linked to respiratory issues and diseases. [9] [10] The LC50 (median lethal dose) for humans has been estimated to be 174 ppm for a 1-hour exposure. [11] It is also included in the NOx family of atmospheric pollutants.

Properties

Nitrogen dioxide is a reddish-brown gas with a pungent, acrid odor above 21.2 °C (70.2 °F; 294.3 K) and becomes a yellowish-brown liquid below 21.2 °C (70.2 °F; 294.3 K). It forms an equilibrium with its dimer, dinitrogen tetroxide (N2O4), and converts almost entirely to N2O4 below −11.2 °C (11.8 °F; 261.9 K). [7]

The bond length between the nitrogen atom and the oxygen atom is 119.7  pm. This bond length is consistent with a bond order between one and two.

Unlike ozone (O3) the ground electronic state of nitrogen dioxide is a doublet state, since nitrogen has one unpaired electron, [12] which decreases the alpha effect compared with nitrite and creates a weak bonding interaction with the oxygen lone pairs. The lone electron in NO2 also means that this compound is a free radical, so the formula for nitrogen dioxide is often written as •NO2.

The reddish-brown color is a consequence of preferential absorption of light in the blue region of the spectrum (400–500 nm), although the absorption extends throughout the visible (at shorter wavelengths) and into the infrared (at longer wavelengths). Absorption of light at wavelengths shorter than about 400 nm results in photolysis (to form NO + O, atomic oxygen); in the atmosphere the addition of the oxygen atom so formed to O2 results in ozone.

Preparation

Industrially, nitrogen dioxide is produced and transported as its cryogenic liquid dimer, dinitrogen tetroxide. It is produced industrially by the oxidation of ammonia, the Ostwald Process. This reaction is the first step in the production of nitric acid: [13]

4 NH3 + 7 O2 → 4 NO2 + 6 H2O

It can also be produced by the oxidation of nitrosyl chloride:

2 NOCl + O2 → 2NO2 + Cl2

Instead, most laboratory syntheses stabilize and then heat the nitric acid to accelerate the decomposition. For example, the thermal decomposition of some metal nitrates generates NO2: [14]

Pb(NO3)2 → PbO + 2 NO2 +1⁄2 O2

Alternatively, dehydration of nitric acid produces nitronium nitrate...

2 HNO3 → N2O5 + H2O
6 HNO3 +1⁄2 P4O10 → 3 N2O5 + 2 H3PO4

...which subsequently undergoes thermal decomposition:

N2O5 → 2 NO2 +1⁄2 O2

NO2 is generated by the reduction of concentrated nitric acid with a metal (such as copper):

4 HNO3 + Cu → Cu(NO3)2 + 2 NO2 + 2 H2O

Selected reactions

Nitric acid decomposes slowly to nitrogen dioxide by the overall reaction:

4 HNO3 → 4 NO2 + 2 H2O + O2

The nitrogen dioxide so formed confers the characteristic yellow color often exhibited by this acid. However, the reaction is too slow to be a practical source of NO2.

Thermal properties

At low temperatures, NO2 reversibly converts to the colourless gas dinitrogen tetroxide (N2O4):

2 NO2 ⇌ N2O4

The exothermic equilibrium has enthalpy change ΔH = −57.23 kJ/mol. [15]

At 150 °C (302 °F; 423 K), NO2 decomposes with release of oxygen via an endothermic process (ΔH = 14 kJ/mol):

2 NO2 →2 NO +  O2

As an oxidizer

As suggested by the weakness of the N–O bond, NO2 is a good oxidizer. Consequently, it will combust, sometimes explosively, in the presence of hydrocarbons. [16]

Hydrolysis

NO2 reacts with water to give nitric acid and nitrous acid:

2 NO2 + H2O → HNO3 + HNO2

This reaction is one of the steps in the Ostwald process for the industrial production of nitric acid from ammonia. [13] This reaction is negligibly slow at low concentrations of NO2 characteristic of the ambient atmosphere, although it does proceed upon NO2 uptake to surfaces. Such surface reaction is thought to produce gaseous HNO2 (often written as HONO) in outdoor and indoor environments. [17]

Conversion to nitrates

NO2 is used to generate anhydrous metal nitrates from the oxides: [15]

MO + 3 NO2 → M(NO3)2 + NO

Alkyl and metal iodides give the corresponding nitrates: [12]

TiI4 + 8 NO2 → Ti(NO3)4 + 4 NO + 2 I2

With organic compounds

The reactivity of nitrogen dioxide toward organic compounds has long been known. [18] For example, it reacts with amides to give N-nitroso derivatives. [19] It is used for nitrations under anhydrous conditions. [20]

Uses

NO2 is used as an intermediate in the manufacturing of nitric acid, as a nitrating agent in the manufacturing of chemical explosives, as a polymerization inhibitor for acrylates, as a flour bleaching agent, [21] : 223  and as a room temperature sterilization agent. [22] It is also used as an oxidizer in rocket fuel, for example in red fuming nitric acid; it was used in the Titan rockets, to launch Project Gemini, in the maneuvering thrusters of the Space Shuttle, and in uncrewed space probes sent to various planets. [23]

Environmental presence

Nitrogen dioxide tropospheric column density in 2011. Aura OMI Nitrogen dioxide troposphere column.png
Nitrogen dioxide tropospheric column density in 2011.

Nitrogen dioxide typically arises via the oxidation of nitric oxide by oxygen in air (e.g. as result of corona discharge): [15]

2 NO + O2 → 2 NO2

NO2 is introduced into the environment by natural causes, including entry from the stratosphere, bacterial respiration, volcanos, and lightning. These sources make NO2 a trace gas in the atmosphere of Earth, where it plays a role in absorbing sunlight and regulating the chemistry of the troposphere, especially in determining ozone concentrations. [24]

Anthropogenic sources

Nitrogen dioxide diffusion tube for air quality monitoring in the City of London. AirQualityLondon1.jpg
Nitrogen dioxide diffusion tube for air quality monitoring in the City of London.

Nitrogen dioxide also forms in most combustion processes. At elevated temperatures nitrogen combines with oxygen to form nitrogen dioxide:

N2 + 2 O2 → 2 NO2

For the general public, the most prominent sources of NO2 are internal combustion engines, as combustion temperatures are high enough to thermally combine some of the nitrogen and oxygen in the air to form NO2. [8]

Outdoors, NO2 can be a result of traffic from motor vehicles. [25] Indoors, exposure arises from cigarette smoke, [26] and butane and kerosene heaters and stoves. [27] Indoor exposure levels of NO2 are, on average, at least three times higher in homes with gas stoves compared to electric stove. [28] [29]

A "fox tail" over Nizhniy Tagil Iron and Steel Works Nizhniy tagil ntmk main entrance.JPG
A "fox tail" over Nizhniy Tagil Iron and Steel Works

Workers in industries where NO2 is used are also exposed and are at risk for occupational lung diseases, and NIOSH has set exposure limits and safety standards. [7] Workers in high voltage areas especially those with spark or plasma creation are at risk.[ citation needed ] Agricultural workers can be exposed to NO2 arising from grain decomposing in silos; chronic exposure can lead to lung damage in a condition called "silo-filler's disease". [30] [31]

Toxicity

Possible pathways implicated in long-term nitrogen dioxide exposure. Dotted lines indicate findings only supported by animal studies, while solid lines indicate findings from controlled human exposure studies. Dashed lines indicate speculative links to asthma exacerbation and respiratory tract infections. ELF = epithelial lining fluid. No2toxpathwaysEPA.png
Possible pathways implicated in long-term nitrogen dioxide exposure. Dotted lines indicate findings only supported by animal studies, while solid lines indicate findings from controlled human exposure studies. Dashed lines indicate speculative links to asthma exacerbation and respiratory tract infections. ELF = epithelial lining fluid.

NO2 diffuses into the epithelial lining fluid (ELF) of the respiratory epithelium and dissolves. There, it chemically reacts with antioxidant and lipid molecules in the ELF. The health effects of NO2 are caused by the reaction products or their metabolites, which are reactive nitrogen species and reactive oxygen species that can drive bronchoconstriction, inflammation, reduced immune response, and may have effects on the heart. [32]

Acute exposure

Acute harm due to NO2 exposure is rare. 100–200 ppm can cause mild irritation of the nose and throat, 250–500 ppm can cause edema, leading to bronchitis or pneumonia, and levels above 1000 ppm can cause death due to asphyxiation from fluid in the lungs. There are often no symptoms at the time of exposure other than transient cough, fatigue or nausea, but over hours inflammation in the lungs causes edema. [33] [34]

For skin or eye exposure, the affected area is flushed with saline. For inhalation, oxygen is administered, bronchodilators may be administered, and if there are signs of methemoglobinemia, a condition that arises when nitrogen-based compounds affect the hemoglobin in red blood cells, methylene blue may be administered. [35] [36]

It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and it is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities. [37]

Long-term

Exposure to low levels of NO2 over time can cause changes in lung function. [38] Cooking with a gas stove is associated with poorer indoor air quality. Combustion of gas can lead to increased concentrations of nitrogen dioxide throughout the home environment which is linked to respiratory issues and diseases. [9] [10] Children exposed to NO2 are more likely to be admitted to hospital with asthma. [39]

Environmental effects

Interaction of NO2 and other NOx with water, oxygen and other chemicals in the atmosphere can form acid rain which harms sensitive ecosystems such as lakes and forests. [40] Elevated levels of NO
2 can also harm vegetation, decreasing growth, and reduce crop yields. [41]

See also

Related Research Articles

<span class="mw-page-title-main">Nitrogen</span> Chemical element with atomic number 7 (N)

Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colourless and odourless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant chemical species in air. Because of the volatility of nitrogen compounds, nitrogen is relatively rare in the solid parts of the Earth.

<span class="mw-page-title-main">Nitric acid</span> Highly corrosive mineral acid

Nitric acid is an inorganic compound with the formula HNO3. It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into oxides of nitrogen. Most commercially available nitric acid has a concentration of 68% in water. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as red fuming nitric acid at concentrations above 86%, or white fuming nitric acid at concentrations above 95%.

<span class="mw-page-title-main">Oxide</span> Chemical compound where oxygen atoms are combined with atoms of other elements

An oxide is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– ion with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 that protects the foil from further oxidation.

The Ostwald process is a chemical process used for making nitric acid (HNO3). The Ostwald process is a mainstay of the modern chemical industry, and it provides the main raw material for the most common type of fertilizer production. Historically and practically, the Ostwald process is closely associated with the Haber process, which provides the requisite raw material, ammonia (NH3). This method is preferred over other methods of nitric acid production, in that it is less expensive and more efficient.

<span class="mw-page-title-main">Oxidizing agent</span> Chemical compound used to oxidize another substance in a chemical reaction

An oxidizing agent is a substance in a redox chemical reaction that gains or "accepts"/"receives" an electron from a reducing agent. In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state, which describes the degree of loss of electrons, of the oxidizer decreases while that of the reductant increases; this is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen, hydrogen peroxide, and the halogens.

<span class="mw-page-title-main">Dinitrogen tetroxide</span> Chemical compound

Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russian rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium mixture with nitrogen dioxide. Its molar mass is 92.011 g/mol.

<span class="mw-page-title-main">Red fuming nitric acid</span> Chemical compound

Red fuming nitric acid (RFNA) is a storable oxidizer used as a rocket propellant. It consists of 84% nitric acid, 13% dinitrogen tetroxide and 1–2% water. The color of red fuming nitric acid is due to the dinitrogen tetroxide, which breaks down partially to form nitrogen dioxide. The nitrogen dioxide dissolves until the liquid is saturated, and produces toxic fumes with a suffocating odor. RFNA increases the flammability of combustible materials and is highly exothermic when reacting with water.

<span class="mw-page-title-main">Nitric oxide</span> Colorless gas with the formula NO

Nitric oxide is a colorless gas with the formula NO. It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its chemical formula. Nitric oxide is also a heteronuclear diatomic molecule, a class of molecules whose study spawned early modern theories of chemical bonding.

Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:

<span class="mw-page-title-main">Dinitrogen pentoxide</span> Chemical compound

Dinitrogen pentoxide is the chemical compound with the formula N2O5. It is one of the binary nitrogen oxides, a family of compounds that contain only nitrogen and oxygen. It exists as colourless crystals that sublime slightly above room temperature, yielding a colorless gas.

The lead chamber process was an industrial method used to produce sulfuric acid in large quantities. It has been largely supplanted by the contact process.

In atmospheric chemistry, NOx is shorthand for nitric oxide and nitrogen dioxide, the nitrogen oxides that are most relevant for air pollution. These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone.

<span class="mw-page-title-main">Zinc nitrate</span> Chemical compound

Zinc nitrate is an inorganic chemical compound with the formula Zn(NO3)2. This colorless, crystalline salt is highly deliquescent. It is typically encountered as a hexahydrate Zn(NO3)2·6H2O. It is soluble in both water and alcohol.

The chemical element nitrogen is one of the most abundant elements in the universe and can form many compounds. It can take several oxidation states; but the most common oxidation states are -3 and +3. Nitrogen can form nitride and nitrate ions. It also forms a part of nitric acid and nitrate salts. Nitrogen compounds also have an important role in organic chemistry, as nitrogen is part of proteins, amino acids and adenosine triphosphate.

<span class="mw-page-title-main">Birkeland–Eyde process</span> Nitrogen fixation process using electrical arcs

The Birkeland–Eyde process was one of the competing industrial processes in the beginning of nitrogen-based fertilizer production. It is a multi-step nitrogen fixation reaction that uses electrical arcs to react atmospheric nitrogen (N2) with oxygen (O2), ultimately producing nitric acid (HNO3) with water. The resultant nitric acid was then used as a source of nitrate (NO3−) in the reaction which may take place in the presence of water or another proton acceptor.

<span class="mw-page-title-main">Reactive nitrogen species</span>

Reactive nitrogen species (RNS) are a family of antimicrobial molecules derived from nitric oxide (•NO) and superoxide (O2•−) produced via the enzymatic activity of inducible nitric oxide synthase 2 (NOS2) and NADPH oxidase respectively. NOS2 is expressed primarily in macrophages after induction by cytokines and microbial products, notably interferon-gamma (IFN-γ) and lipopolysaccharide (LPS).

<span class="mw-page-title-main">Nitrate radical</span> Chemical compound

Nitrogen trioxide or nitrate radical is an oxide of nitrogen with formula NO
3, consisting of three oxygen atoms covalently bound to a nitrogen atom. This highly unstable blue compound has not been isolated in pure form, but can be generated and observed as a short-lived component of gas, liquid, or solid systems.

<span class="mw-page-title-main">Dinitrogen trioxide</span> Chemical compound

Dinitrogen trioxide is the inorganic compound with the formula N2O3. It is a nitrogen oxide. It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C (−6 °F):

<span class="mw-page-title-main">Zirconium nitrate</span> Chemical compound

Zirconium nitrate is a volatile anhydrous transition metal nitrate salt of zirconium with formula Zr(NO3)4. It has alternate names of zirconium tetranitrate, or zirconium(IV) nitrate.

<span class="mw-page-title-main">Transition metal nitrate complex</span> Compound of nitrate ligands

A transition metal nitrate complex is a coordination compound containing one or more nitrate ligands. Such complexes are common starting reagents for the preparation of other compounds.

References

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  2. 1 2 3 4 Haynes, 4.79.
  3. ↑ Mendiara, S. N.; Sagedahl, A.; Perissinotti, L. J. (2001). "An electron paramagnetic resonance study of nitrogen dioxide dissolved in water, carbon tetrachloride and some organic compounds". Applied Magnetic Resonance. 20 (1–2): 275–287. doi:10.1007/BF03162326. S2CID   97875925.
  4. ↑ Haynes, 4.134.
  5. ↑ Haynes, 5.16.
  6. 1 2 "Nitrogen dioxide". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  7. 1 2 3 4 5 NIOSH Pocket Guide to Chemical Hazards. "Nitrogen dioxide". National Institute for Occupational Safety and Health (NIOSH).
  8. 1 2 PD-icon.svg This article incorporates public domain material from Nitrogen dioxide. United States Environmental Protection Agency. Feb 23, 2016.
  9. 1 2 "Clearing the Air: Gas Cooking and Pollution in European Homes". CLASP. 8 November 2023. Retrieved 2024-05-05.
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  16. ↑ physical chemistry
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  39. ↑ Wang, Weiyi; Gulliver, John; Beevers, Sean; Freni Sterrantino, Anna; Davies, Bethan; Atkinson, Richard W.; Fecht, Daniela (2024). "Short-Term Nitrogen Dioxide Exposure and Emergency Hospital Admissions for Asthma in Children: A Case-Crossover Analysis in England". Journal of Asthma and Allergy. 17: 349–359. doi: 10.2147/JAA.S448600 . ISSN   1178-6965. PMC   11016460 . PMID   38623450.
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  41. ↑ "Nitrogen oxides". Queensland Government. Retrieved 2020-07-03.

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